Device for dry forming a web of fibers

ABSTRACT

What is described is a device for dry forming a web of fibers, comprising: a fiber distribution head ( 1 ); a forming wire ( 3 ) movable under said head; a suction means ( 5 ) located on the opposite side of said forming wire from said head; within said head, a chamber ( 9 ) into which a flow of gas, in which said fibers are suspended, is directed, the chamber having a buttom opening ( 9 A) closed by a screen mesh ( 17 ) which is essentially parallel to said forming wire ( 3 ) and which faces the latter; and agitator members ( 45 ) inside said chamber, above said screen mesh ( 17 ), for agitaing and distributing the fibers. Characteristically, the screen mesh ( 17 ) is a continuous mesh, movable along a closed path around said chamber, the portion of said mesh parallel to and facing the forming wire moving along a path which is essentially parallel to said forming wire. Additionally, the agitator members comprise a plurality of rotating shafts ( 47 ) which are parallel to each other and othogonal to the direction of advance (f 3 ) of said forming wire.

TECHNICAL FIELD

The present invention relates to a device for producing a web or sheetof fibrous material by a dry method, in other words without using awater-based fiber stock.

PRIOR ART

Webs or sheets of fibrous material, particularly paper, absorbent paper,or what is known as “tissue paper”, are normally produced by means ofprocesses and machines in which a water-based stock of cellulose fibersis distributed on a forming screen to form a thin web. This web is thendried by suction to remove the water and by subsequent passage over aheated roller or other drying device.

In relatively recent times, a new process was introduced for producingpaper, particularly very thick absorbent paper, for example for theproduction of sanitary articles such as diapers for infants or sanitarypads. In this process, a web of fibers supplied by a flow of air isdistributed on a forming screen or wire. This is known as the “airlaid”process.

Devices of various types have been designed for carrying out the dryforming process, in order to make the distribution of fibers as uniformas possible, and in order to overcome many of the drawbacks and problemsof this new method.

In general, airlaid webs are produced by suspending the fibers in a flowof air and depositing them on a forming mesh or screen, under whichsuction is applied to guide the fibers which are supplied from a forminghead placed above. The fibers are distributed in the flow of air byvarious methods.

A first category of devices uses a forming head with a mesh screenlocated under it, through which the fibers are drawn by a flow of air. Aforming wire runs under the mesh screen which closes the underside ofthe forming head, and the fibers are deposited on the forming wire toform the web. Above the screen closing the underside of the forming headthere are propellers rotating about vertical axes, in other words axesorthogonal to the forming wire and to the screen. The fibers are drawnby a flow of air through the screen closing the head and are depositedon the forming wire. Examples of devices made in this way are describedin GB-1499687; GB-1559274; U.S. Pat. No. 3,581,706; U.S. Pat. No.4,014,635; U.S. Pat. No. 4,157,724; U.S. Pat. No. 4,276,248; U.S. Pat.No. 4,285,647; U.S. Pat. No. 4,335,066; U.S. Pat. No. 4,351,793; U.S.Pat. No. 4,482,308; U.S. Pat. No. 4,494,278; U.S. Pat. No. 4,627,953;U.S. Pat. No. 5,527,171; U.S. Pat. No. 5,471,712; WO-A-9105100;WO-A-9522656; WO-A-9610663; WO-A-9954537; EP-B-616056.

A second type of device for distributing the fibers in the flow of airwhich is sucked through the forming wire makes use of one or moreperforated pipes with axes parallel to the forming wire. The fibersdrawn by the air emerge from the holes in the pipes and are deposited onthe underlying forming wire, which advances in the direction of feeding.EP-A-032772 describes a forming head of this type. A pair of tubes withparallel axes is positioned above the forming wire. The tubes haveperforated walls through which the fibers pass out, the fibers beingcarried by a flow of air inside said tubes. To promote the outflow ofthe fibers and to prevent their accumulation inside the tubes, rotatingshafts, having their axes parallel to the tubes and having radialpoints, are fitted in the tubes. The points have the additional functionof disintegrating any lumps of fibers which form in the flow of aircarrying them. Devices based essentially on the same principle aredescribed in U.S. Pat. No. 4,352,649, WO-A-8701403 and EP-B-188454. Inthese devices, the forming head has no screen closing its underside, andthe flow of air and suspended fibers is confined to the interior of thepipes with perforated walls, where the perforated wall has the samefunction as the screen closing the heads of the first type mentionedabove.

U.S. Pat. No. 6,233,787 describes a device for dry forming a web offibers in which a head which receives a flow of air with the suspendedfibers is positioned above the forming wire. The head has in its lowerpart a set of rotating shafts or rollers, with axes parallel to eachother and to the forming wire, and extending transversely with respectto the direction of advance of the forming wire. The shafts or rollershave radial points or rods which extend in such a way that theyessentially close the lower aperture of the head, forming a kind ofpermeable wall which permits the passage of the fibers which are drawnby the flow of air sucked from below the forming head.

EP-A-159618 describes a device for dry forming a web of fibers,comprising a forming head located above the forming screen through whichis sucked the flow of air which draws the fibers. The bottom of theforming head is closed by a fixed screen, which is perforated to allowthe passage of the fibers. Above the fixed screen there is a pluralityof rollers having axes parallel to the forming screen and orthogonal tothe direction of advance of the latter. The rollers are equipped withradial points and are supported by a continuous conveyor which movesthem in a direction parallel to the direction of advance of the formingscreen.

OBJECTS AND SUMMARY OF THE INVENTION

The object of the present invention is to provide a new type of devicefor producing sheets or webs of fiber material by a dry forming processwhich is particularly efficient and enables high-quality material to beproduced.

This and other objects and advantages, which the following text willmake clear to those skilled in the art, are essentially achieved with adevice for dry forming a web of fibers, comprising: a fiber distributionhead; a forming wire movable under said head; a suction means located onthe opposite side of said forming wire from said head; within said head,a chamber into which a flow of gas (particularly air), in which saidfibers are suspended, is directed, the chamber having a bottom openingclosed by a screen mesh which is essentially parallel to said formingwire and which faces the latter; and agitator members inside saidchamber, above said screen mesh, for agitating and distributing thefibers. Characteristically, the screen mesh is made to be continuous andmovable along a closed path around said chamber, the portion of saidmesh parallel to and facing the forming wire moving along a path whichis essentially parallel to said forming wire. Additionally, the agitatormembers comprise a plurality of rotating shafts which are parallel toeach other and orthogonal to the direction of advance of the formingwire, said shafts being provided with shaped profiles to agitate thefibers in the chamber.

The chamber is essentially closed off from the external environment,except at the bottom opening, past which the screen mesh runs. Thus awell-controlled flow of air and suspended fibers is generated, this flowbeing intercepted by the forming wire on which the web of fibers isformed. This web is subsequently consolidated in various ways, by knownmethods. The presence of a movable screen mesh and agitator membersrotating about axes parallel to each other and to the plane of thescreen mesh and consequently to the forming wire makes the deviceparticularly efficient and suitable for forming a uniform web.

In a preferred embodiment of the invention, in order to feed the flow ofair and suspended fibers into the chamber of the forming head, aplurality of diffusers is advantageously provided above the agitatormembers, the diffusers being provided with outlets, facing said agitatormembers, for the admission of said flow of air and fibers. The admissionoutlets can be made in a shape which is elongated, for example in adirection parallel to the axes of rotation of the agitator members. Thediffusers can be aligned parallel to the axes of rotation of theagitator members. The distance between the inlet apertures, their sizeand their distance from the screen mesh are parameters which are chosenin such a way that the flows generated by the various aligned aperturesintersect each other above the screen mesh. This provides a greaterregularity of the thickness of the web formed on the forming wire.

In order to eliminate the lumps which may form in the chamber of theforming head, in an advantageous embodiment of the device suctionmembers are associated with the chamber for sucking in and recycling thelumps. The lumps are then sent to known means which disintegrate themand recover the fibers which are reintroduced into the flow of air fedto the forming head.

In a particularly advantageous embodiment of the present invention, thesuction members comprise at least one set of suction inlets adjacent toeach other along a direction of alignment which is transverse withrespect to the direction of advance of said forming wire. Preferably,two sets of suction inlets are provided, in the proximity of theupstream and downstream ends of the chamber with respect to thedirection of advance of the screen mesh. These are the areas most likelyto contain accumulations of lumps, which are thus promptly removed andrecycled.

The agitator members can be rotated by a single motor unit. However, ina preferred embodiment of the invention, a plurality of independentmotors can be provided, for groups of agitator members for example.Preferably, each agitator member comprises its own independent motor.The motors can be bidirectional, to enable the direction of rotation ofthe agitator members to be reversed. When an independent motor isprovided for each agitator member, the velocity and direction ofrotation of each agitator member can be controlled independently of theothers.

The shaped profiles of the shafts of the individual agitator members canadvantageously have a pointed configuration. They can be formed, forexample, in a shape-approximating to an isosceles triangle, with thesides converging toward the vertex of the triangle being curved insteadof straight and, in particular, concave toward the outside of thetriangle. Additionally, the shaped piece preferably lies on acylindrical surface whose axis coincides with the axis of rotation ofthe shaft of the corresponding agitator member. The various shapedprofiles can be supported on and integral with disks keyed on the shaftsof the agitator members. Each disk has one or preferably two profiles.

In order to obtain a particularly regular flow of air and fibers towardthe screen mesh, a compartment for the introduction of an auxiliary flowof gas (particularly air) can be provided above the chamber into whichthe diffusers carrying the fibers suspended in the flow of air open, andholes can be made in a separating partition which divides thecompartment from the chamber, to allow said auxiliary flow to pass fromthe compartment to the chamber. The auxiliary flow of air can besuitably controlled in respect of temperature and/or humidity, to ensureoptimal conditions for forming the web. The velocity of the auxiliaryflow and consequently the total quantity of air entering the chamber andpassing out through the screen mesh can also be controlled, by adjustingthe auxiliary flow and also if necessary the flow of air carrying thefibers which enters the chamber through the aforesaid diffusers.

In an advantageous embodiment of the device, the distance of the screenmesh from the agitator members is made adjustable, thus allowing themodification of the web forming conditions and consequently thecharacteristics of the product. For this purpose, the portion of saidscreen mesh forming the bottom closure of the chamber is advantageouslyguided by guide members whose distance from the agitator members isadjustable. These guide members can comprise, for example, an upperframe and a lower frame, essentially parallel to and spaced apart fromeach other, through which said screen mesh passes. The frames aresupported in a position which is adjustable with respect to the agitatormembers. The frames advantageously have guide members for the screenmesh, and, in order to prevent or at least reduce the suction of airfrom the outside toward the forming wire, extendable sealing means canadvantageously be provided between the guide members and the chamber ofthe forming head, these sealing means adapting themselves to theposition taken up by the screen mesh with respect to the agitatormembers. Adjustable sealing means can also be provided between the guidemembers and the forming wire.

Further advantageous characteristics and embodiments of the inventionare indicated in the attached claims and in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more clearly understood from the description andthe attached drawing, which shows a practical and non-restrictiveembodiment of the invention. In the drawing, in which identical numbersindicate identical or corresponding parts,

FIG. 1 shows a perspective view of the forming head;

FIG. 2 shows a perspective view of one of the agitator members;

FIG. 3 shows a side view taken through III-III in FIG. 5;

FIG. 4 shows a front view taken through IV-IV in FIGS. 3 and 5;

FIG. 5 shows a plan view taken through V-V in FIGS. 3 and 4;

FIG. 6 shows a section according to a vertical plane indicated by VI-VIin FIG. 4;

FIG. 7 shows an enlargement of the detail VII of FIG. 6;

FIG. 8 shows an enlargement of the detail VIII of FIG. 6; and

FIG. 9 shows a perspective view of the detail of FIG. 8.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION

The device comprises, in a general way, a forming head, indicated as awhole by 1, and a forming wire 3, shown in particular in FIGS. 6 and 7and omitted for the sake of simplicity in the other figures. A suctionbox 5 is positioned under the forming wire 3, in other words on theopposite side of the wire to that on which the forming head 1 islocated. As described more fully below, a flow of air is fed into theforming head and draws with it fibers of cellulose or of other suitablematerial. The flow is sucked by the suction box 5, and the fibers areintercepted by the forming wire 1, thus generating on the screen a web Vof fibers (FIG. 7), which is subsequently consolidated In a known way.The forming wire 3 advances in the direction of the arrow f3.

The head 1 has a supporting structure 7 inside which is positioned achamber 9 into which the flow of air and suspended fibers is fed. Thechamber 9 is of essentially parallelepipedal shape, delimited by fourvertical walls and a top wall 11. The wall 11 forms a partition whichseparates the chamber 9 from a compartment 13 located above. Holes 11Aare made in the wall 11 to bring the compartment 13 into communicationwith the chamber 9. An air supply pipe 14 opens into the compartment 13.The air introduced by the pipe 14 has controlled temperature andhumidity, and penetrates into the underlying chamber 9 through the holes11A in the wall or dividing partition 11.

From the wall 11 there extend towards the interior of the chamber 9diffusers 15 terminating in outlets or nozzles 15A having a taperedshape elongated in a direction orthogonal to the direction of advance f3of the forming wire 3. The diffusers 15 are positioned in four rowsorthogonal to the direction of advance f3 of the forming wire 3. Theyare connected to two manifolds for the introduction of the flow of airand fibers, indicated by 18A and 18B, which are supplied by known meanswhich are not shown. In practice, each of the two manifolds 18A and 18Bsupplies two rows of diffusers 15.

The chamber 9 is open at its bottom, and a screen mesh 17 runs past theopening 9A (FIG. 7) and extends along a closed path around said chamber9. The path is delimited by rollers 19, 21, 23, 25, 27 and 29. Theroller 25 is powered by a motor 31 and transmits the motion to thescreen mesh 17, which moves continuously in the direction of the arrowf17. In the illustrated example, the portion of mesh which closes thebottom of the chamber 9 and is parallel to the forming wire 3 advancesin the opposite direction to the direction of advance of said wire,although it would also be possible to make it advance in the samedirection. The roller 19 is supported by a pair of movable oscillatingarms 33 acted on by cylinder and piston actuators 35 which keep thescreen mesh 17 under tension. The roller 27 is associated with knownmeans 37 which modify the position of the axis of said roller to keepthe screen mesh correctly guided.

The lower rollers 21 and 23, between which extends the lower branch ofthe screen mesh 17 closing the bottom opening of the chamber 9, havemovable axes, and their position with respect to the bottom opening ofthe chamber 9 can be adjusted to modify the position of the screen meshwith respect to the agitator members which are located within thechamber 9 and which are described below.

The structure 7 of the forming head 1 carries a set of supports 41 and43, which support agitator members indicated as a whole by 45. One ofsaid agitator members is shown in isolation and in a perspective view inFIG. 2. Each agitator member comprises a shaft 47, extendingtransversely with respect to the direction of advance of the formingwire 3 and of the screen mesh 17, and supported by a pair of supports 41and 43. Each support 43 is associated with an independent variable-speedbidirectional motor 46, which rotates the corresponding shaft 47.

A plurality of disks 49 is keyed on each shaft 47. Two shaped profiles51 are fixed on the circular edge of each disk 49. Each shaped piece hasa pointed configuration, and consists essentially of three sidesarranged in the form of an isosceles triangle whose vertex forms theaforesaid point. The sides converging on the vertex are curved, with theconcavity facing the outside of the triangle. The triangle lies on atheoretical cylindrical surface coaxial with the corresponding shaft 47.The points formed by the two shaped profiles 51 integral with a singledisk 49 are orientated in the same direction. In a different embodimentwhich is not illustrated, each shaped piece is double and symmetricaland has two opposed points, to produce the same effect on the fiberseven when the direction of rotation is reversed.

As shown in particular in the section in FIG. 6, the end walls 9P of thechamber 9, in other words those orthogonal to the direction of advancef3 of the forming wire 3, terminate at their bases in a casing 9B whichpartially encloses the outer two agitator members 45. Two deflectors 9Dextend into the chamber 9 above these outer agitator members. The lowerpart 9B and 9C of the end walls 9P and the deflectors 9D delimit theinlet area of two sets of suction inlets 53. The suction inlets 53 arearranged in two alignments which are transverse with respect to thedirection of advance of the forming wire 3, adjacently to the outer twoagitator members 45. In the illustrated example, six suction inlets 53are provided for each set. The six suction inlets of each set areconnected to a corresponding manifold 55 and the two manifolds 55 areconnected to a suction pipe 57. A recycling air flow is sucked throughthis pipe and draws with it the lumps of fibers which have not passedthrough the screen mesh 17. The recycling air flow is sent to means ofbreaking the lumps and recovering the fibers, these means being knownand not illustrated.

Between the return roller 23 and the corresponding end wall 9P, 9B, 9Cof the chamber 9 there is positioned a suction member 61 which extendsacross the whole width of the screen mesh 17 and which is locatedadjacent to the inner surface of the screen mesh, in other words thesurface facing the interior of the closed path of said mesh. The suctionmember 61 has the function of removing from the mesh any residues offibers still adhering to it. It is connected to a suction pipe 63.

A suction member 65 connected to a suction pipe 67 is located outsidethe path of the screen mesh 17, between the return roller 23 and thereturn roller 25. The suction member 65 extends across the width of thescreen mesh 17 and sucks away any fibers or residues adhering to saidmesh.

The return roller 23 is associated with a doctor blade 71 which detachesany detritus or residues of fibers which may have been transferred fromthe screen mesh to the roller and remain adhering to said roller.

As shown in particular in FIGS. 3, 6 and 9, the return rollers 21 and 23are supported by two pairs of supports 73 and 75, fixed to two pairs ofplates 77 and 79. Each pair of plates 77 and 79 is integral with across-member 81 which extends parallel to the direction of advance f3 ofthe forming wire 3. Each of the plates 77 and 79 is fixed to the fixedstructure 7 by clamping screws 83 (FIG. 9) which are inserted intoslotted holes 85 in said plates and are engaged in threaded holes (notvisible) formed in a plate 7A forming part of the supporting structure7. When the screws 83 are slackened, each of the plates 77 can be madeto slide vertically, by means of an adjusting screw 87 engaged in a nut89 integral with the corresponding plate 77 and supported by a block 91integral with the structure 7. Thus it is possible to adjust theposition of the pair of rollers 21 and 23 and consequently the positionof the screen mesh 17 with respect to the structure 7 and therefore withrespect to the agitator members 45.

The portion of the screen mesh 17 extending under the opening 9A of thechamber 9 is guided between two frames 93 and 95, these being the upperand lower frames respectively (see, in particular, FIG. 7). The twoframes 93 and 95 are integral with the cross-members 81 and theirvertical position is therefore adjustable. Each frame is formed fromfour square metal sections arranged in a rectangle, the sections formingthe upper frame 93 having a smaller cross-section than that of thesections forming the lower frame 95. On the lower surface of the upperframe 93 there are fitted guide sections 97 which have a lower flange97A for the actual guiding, parallel to the screen mesh 17, and a flange97B orthogonal to the screen mesh 17, which extends parallel to aterminal wall 9E which delimits the opening 9A of the chamber 9. The twosections 97B and 9E which are parallel to each other form a kind of wallwhich can be telescopically extended and contracted when thecross-members 81, and consequently the two frames 93 and 95, are loweredand raised. This extendable and contractible wall forms a sealing systemwhich prevents or at least drastically reduces the suction of air fromthe outside toward the suction box 5 located under the forming wire 3.

A guide section 99 with a horizontal flange 99A parallel to the flange97A, and a vertical flange 99B, is fitted on the upper surface of thelower frame 95. Four lengths of metal section 99 welded along the foursides of the frame 95 form, with their respective flanges 99B, an outletessentially corresponding to the opening of the chamber 9 located above.A box 101 is fitted around the outlet formed by the sections 99, and itsposition with respect to the frame 95 and to the sections 99 can beadjusted by means of a system of tightening screws and slots. The box101 is open at its top toward the screen mesh 17 and at its bottomtoward the forming wire 3, and delimits the space through which the flowof air and fibers leaving the screen mesh 17 reaches the forming wire 3as a result of the suction applied by the suction box 5. Since theposition of the box 101 can be adjusted with respect to the frame 95,the lower edge of said box can be positioned as closely as possible tothe forming wire 3, thus reducing the passage cross section of the airsucked in from the outside through the forming wire 3.

With this particular arrangement, the distance of the screen mesh 17from the agitator members 45 can be adjusted while the space under theopening 9A of the chamber 9, between said chamber and the forming wire,is kept essentially sealed, regardless of the position of the screenmesh.

The operation of the device described up to this point is as follows.The forming wire 3 is made to move, by means of powered and returnrollers, which are not shown and which are of known types, in such a waythat it passes under the forming head 1 at an essentially uniformvelocity. The pressure in the suction box 5 is reduced. A flow of airwith suspended fibers is fed into the chamber 9 of the forming head 1through the manifolds 18A and 18B and the diffusers 15. In addition tothe main flow from the diffusers 15, in which the fibers are suspended,a secondary air flow is blown into the chamber 9 through the pipe 14 andthe compartment 13. The agitator members 45 are rotated, normally all atthe same velocity and in a direction of rotation such that the points ofthe shaped profiles 51 have a tangential velocity essentially matchingthe direction of advance of the screen mesh 17 and the forming wire 3.Thus the fibers located nearest to the screen mesh are pushed by theconcave portions of the profiles 51 towards the sides of the chamber andare distributed uniformly over the surface of the mesh facing themthrough the opening 9A of the chamber 9. Additionally, the movement ofthe profiles 51 in the upper part of their path creates turbulence inthe flow of air and fibers, thus providing a better and more uniformdistribution of the fibers in the space of the chamber 9, and alsopreventing the formation of lumps.

By suitably programming the control unit of the forming head, thevelocity of rotation of the individual agitator members 45 can bemodified, and the direction of rotation of one or more of them can alsobe reversed if necessary.

The suction inlets 53 are kept at slightly reduced pressure and suck inthe lumps of fibers which reach the front and rear ends of the chamber 9(with respect to the direction of advance of the forming wire 3) andenable the fibers forming these lumps to be recovered and recycled afterdissolution of said lumps.

It should be understood that the drawing shows only one possibleembodiment of the invention, which can be varied in its forms andarrangements without departure from the scope of the essential conceptof the invention. The presence of reference numbers in the attachedclaims has the sole purpose of facilitating the reading of the claimswith reference to the preceding description and the attached drawings,and does not in any way limit the protective scope of the claims.

1. Device for dry forming a web of fibers, comprising: a fiber distribution head; a forming wire movable under said head; a suction means located on the opposite side of said forming wire from said head; within said head, a chamber into which a flow of gas, in which said fibers are suspended, is directed, the chamber having a bottom opening closed by a screen mesh which is essentially parallel to said forming wire and which faces the latter; and agitator members inside said chamber, arranged directly above said screen mesh for agitating and distributing the fibers on the surface of said screen mesh facing the interior of said chamber; characterized in that: said screen mesh is made to be continuous and movable along a closed path around said chamber, the portion of said mesh parallel to and facing the forming wire moving along a path which is essentially parallel to said forming wire; and said agitator members comprise a plurality of rotating shafts which are parallel to each other and to the screen mesh and orthogonal to the direction of advance of said forming wire, said shafts being provided with shaped profiles to agitate the fibers in said chamber.
 2. Device according to claim 1, characterized in that a plurality of diffusers opens into said chamber, these diffusers being positioned above the agitator members and being provided with outlets facing said agitator members, for the admission of said flow of gas and fibers.
 3. Device according to claim 1, characterized in that said chamber is associated with suction members for sucking in and recycling lumps of fibers which do not pass through said screen mesh.
 4. Device according to claim 3, characterized in that said suction members comprise at least one set of suction inlets adjacent to each other along a direction of alignment which is transverse with respect to the direction of advance of said forming wire.
 5. Device according to claim 4, characterized in that said at least one set of suction inlets is aligned parallel to the axes of rotation of said agitator members.
 6. Device according to claim 4, characterized in that it comprises two sets of suction inlets located at two opposite ends of the chamber along the direction of advance of the screen mesh.
 7. Device according to claim 1, characterized in that said agitator members comprise independent motors (46).
 8. Device according to claim 7, characterized in that said independent motors are bidirectional.
 9. Device according to claim 1, characterized in that said shaped profiles (51) carried by said shafts have a configuration with at least one point.
 10. Device according to claim 1, characterized in that each of said agitator members comprises a shaft on which is keyed a plurality of disks each of which carries at least one of said shaped profiles.
 11. Device according to claim 10, characterized in that each of said profiles has at least one configuration essentially in the form of an isosceles triangle, lying on a cylindrical surface, their sides which converge on the vertex being curved and having their concavity facing the outside of the triangle to form a point.
 12. Device according to claim 10, characterized in that each of said disks is associated with at least two of said shaped profiles, each of which has at least one point.
 13. Device according to claim 1, characterized in that a compartment for the introduction of an auxiliary flow of gas is provided above the chamber, holes being made in a separating partition which separates said compartment from said chamber, to allow said auxiliary flow of gas to pass from the compartment to the chamber.
 14. Device according to claim 2, characterized in that said diffusers extend from said separating partition towards the interior of the chamber.
 15. Device according to claim 2, characterized in that said diffusers are arranged in alignments essentially parallel to the axes of said agitator members.
 16. Device according to claim 2, characterized in that said diffusers terminate in outlets elongated in a transverse direction with respect to the direction of advance of said forming wire, and in that the apertures of said outlets and their distance from the screen mesh are such that the jets of gas and suspended fibers from adjacent outlets intersect above the screen mesh.
 17. Device according to claim 1 characterized in that the distance of said screen mesh from the agitator members is adjustable.
 18. Device according to claim 1, characterized in that a portion of said screen mesh, forming the bottom closure of said chamber, is guided by guide members whose distance from the agitator members is adjustable.
 19. Device according to claim 18, characterized in that said guide members comprise an upper frame and a lower frame, essentially parallel to each other and spaced apart from each other, through which said screen mesh passes.
 20. Device according to claim 19, characterized in that said upper and lower frames are supported in a position which is adjustable with respect to the position of the agitator members.
 21. Device according to claim 20, characterized in that said upper and lower frames are supported by a sliding block which can be adjusted and clamped on the supporting structure of said head.
 22. Device according to claim 21, characterized in that said sliding block supports at least two return rollers of said screen mesh between which extends said portion of the screen mesh which closes the bottom of said chamber.
 23. Device according to claim 19, characterized in that said upper frame is integral with a guide section for said screen mesh.
 24. Device according to claim 19, characterized in that said lower frame is integral with a guide section for said screen mesh.
 25. Device according to claim 18, characterized in that extendable seating means are positioned between said guide members and the chamber of said forming head.
 26. Device according to claim 19, characterized in that said extendable sealing means comprise a section integral with said upper frame and interacting with a perimetric edge surrounding the bottom opening of said chamber.
 27. Device according to claim 18, characterized in that adjustable sealing means are provided between said guide members and said forming wire.
 28. Device according to claim 19, characterized in that said adjustable sealing means comprise a box open above and below, towards said screen mesh and towards said forming wire, supported by said lower frame.
 29. Device according to claim 1, characterized in that it comprises internal cleaning means for cleaning the surface of the screen mesh facing said chamber.
 30. Device according to claim 29, characterized in that said internal cleaning means are suction means.
 31. Device according to claim 1, characterized in that it comprises external cleaning means for cleaning the surface of the screen mesh facing the forming wire.
 32. Device according to claim 31, characterized in that said external cleaning means are suction means.
 33. Device according to claim 1, characterized in that said screen mesh runs around a plurality of return rollers located around said chamber and outside it, at least one of these rollers being powered.
 34. Device according to claim 33, characterized in that at least one of the return rollers located directly downstream from the bottom opening of the chamber with respect to the direction of advance of said screen mesh is associated with doctor blade means for removing any detritus adhering to said roller.
 35. Device according to claim 33, characterized in that at least one of said return rollers is supported in a movable way for tensioning said screen mesh.
 36. Device according to claim 33, characterized in that at least one of said return rollers is associated with means of aligning the screen mesh.
 37. Device according to claim 13, characterized in that the assembly formed by said chamber and said compartment is delimited outwardly by a box which is open only next to said screen mesh.
 38. Device according to claim 10, characterized in that each of said shaped profiles is symmetrical and has two points orientated in two opposed directions in the tangential direction of said disks. 